MEPS 151:81-90 (1997)  -  doi:10.3354/meps151081

The effect of solar radiation on photosynthesis, quantum yield of fluorescence and pigmentation under solar radiation in a laboratory system and in the natural habitat during a daily cycle was investigated in the red eulittoral alga Porphyra leucosticta. Optimal (F_v/F_m) and effective (DeltaF/F_m') quantum yield of fluorescence, photosynthetic efficiency and maximal photosynthesis were drastically reduced by UV-B (280-315 nm) radiation in algae transferred from the laboratory (grown in white light) to solar radiation for 3 h. The absorptance due to chlorophyll and biliproteins (phycoerythrin and phycocyanin) increased after 3 h of incubation in photosynthetically active radiation (PAR, 400-700 nm) and PAR+UV-A (315-400 nm) whereas no changes were observed under PAR+UV-A+UV-B. In the field, the effective quantum yield and oxygen production decreased at noon during a daily cycle, indicating photoinhibition. When solar UV-A and UV-B radiation was removed by means of selective filters, the average effective quantum yield increased by 28 ± 2% SD. Chlorophyll and biliprotein concentration presented a daily pattern which was affected by UV radiation. Both chlorophyll and biliprotein contents were reduced at noon, followed by recovery in the afternoon, but only when UV radiation was cut off. The difference between the maximal and minimal chl a concentration during the daily cycle was greater in the presence of UV radiation, but the difference for phycoerythrin and phycocyanin was greater under PAR alone. These results seem to indicate that the accumulation of pigments is affected by solar radiation, with short-term changes induced by UV light. The ecological relevance of the daily variations of photosynthesis and pigmentation under solar radiation is discussed.

Biliproteins · Chlorophyll · Daily cycle · PAM fluorescence · Photosynthesis · Porphyra leucosticta